Missing Values

It is possible to assign a missing value as part of an Automatic Variable calculation and for data collected via the Data Entry Module. These missing values can be used in automatic numeric calculations, skip conditions, and edit conditions (see Using Special Codes and Missing Values in QDS Expressions).

Automatic Variables

The constant .MSG can be assigned to an Automatic Variable which QDS stores as a range of values; display value [empty].

Examples:

  • IF (condition, .MSG,2,3) returns “[Empty]” if the condition is TRUE
  • IF (condition, .MSG,"Eligible") returns “[Empty]” if the condition is TRUE
  • IF (VAR = .MSG,…) returns TRUE if the VAR is equal to “[Empty]”
  • IF (VAR ^= .MSG,…) returns TRUE if the VAR is not equal to “[Empty]”

In the Warehouse Manager, values of .MSG will have a Numeric Code of 0, Display Value of [Empty] and a Range of -99 to 100.

In Warehouse Manager, values of .MSG

In most cases, if another calculation is performed on a .MSG value, the result will be “Undefined”, as an “empty” response is a range of values. In the Warehouse Manager, this will be displayed as a Numeric Code of -1, Display Value of [Undefined] and a Range of 9801 to 10000.  

Values if another calculation is performed on a .MSG value

Tip: When .MSG values are exported from the Warehouse Manager, “empty” responses are output as system missing specific to the data analysis software, such as “.” in SAS or Stata.

Paper Questionnaire Data

For data collected with the Data Entry Module there is an additional Special Code option of Missing. This could be used if one or more answer(s) on a form were simply left blank and it is not possible to tell whether they were refused or simply missed.

If you choose to allow missing values in your Data Entry control file you can enter a “Missing” code which will be displayed and recorded as “.” (See Entering missing values under Entering Data).

Whether or not your QDE program allows missing values is determined on Data Entry Module Build Options. Note that, by default, missing values are not allowed. If missing values are allowed, any item that is not an identifier variable may be recorded as missing.

In the Warehouse Manager, results for a Missing value for Data Entry are:

  • Numeric code 0
  • Display [Empty]
  • Minimum <minimum allowed response>
  • Maximum <maximum allowed response>